The present invention relates generally to information networks and more particularly to an improved configuration system that will allow hosts and routers to configure themselves automatically.
With the proliferation of network attached appliances and inexpensive computing devices there is an increasing demand for internetworking among these devices. It is anticipated that such devices will be interconnected to form ad-hoc, dynamic networks, with frequent disconnections and reconnections of devices to and from the network, and frequent changes in the network topology. Ideally, networking in such an environment should be done without any user intervention or administration. The term “zero-configuration networking” is sometimes used to describe this new paradigm of networking.
Zero-configuration networking has proven challenging to implement, particularly where the network consists of multiple routers connecting various segments. Generally speaking, a zero-configuration network should satisfy the following properties:                absence of administration: the system should enable networking in the absence of configuration and administration. In this regard, so called Dynamic Host Configuration Protocols (DHCP) and Domain Name Servers (DNS) and Multi-Cast Address Dynamic Client Allocation Protocol (MADCAP) fall short in that each of these requires an administrator to set up or configure the server before it can be used.        Co-existence and transition: a zero-configuration protocol in one area may need to co-exist with a non-zero configuration protocol from another area. For example, a host might be using a non-zero configuration protocol for IP host configuration (such as DHCP) but a zero-configuration protocol for name-to-address translation. Preferably, the zero configuration protocol should revert to an administered protocol if such an administered protocol exists. This also means that a zero configuration protocol and a non-zero configuration protocol for the same area cannot co-exist within a zero configuration network. For example, assume that a host is using a zero configuration protocol for IP host configuration. If an administrator installs a DHCP server into the network, the host must reconfigure to use the DHCP server. The reverse transition from an administered mode to a zero configuration mode must also exist.        Interoperability: Zero configuration protocols should be based on the existing administered protocols as much as possible for maximum interoperability.        
The above properties have implications in one or more of the following areas of networking:                1. IP Host Configuration: A host automatically gets its IP address, netmask, default router address, DNS server address. In this regard, DHCP is the administered IP host configuration protocol.        2. Name-To-Address Translation: A host can translate between name and address of other hosts without any user intervention. Note, DNS is the administered name-to-address translation protocol.        3. Automatic Allocation Of Multicast Addresses: Hosts can agree on a multicast address without any user administration.        4. Service Discovery: A host is able to discover all the services (e.g., printing, faxing, storage) available within the network.        
To appreciate why zero configuration networking is challenging in a multirouter network, consider FIGS. 1a and 1b. Assume that router R1 and router R2 are stand-alone routers which are initially disconnected and subsequently connected as at X. Prior to connection at X, the respective routers perform initialization which assigns subnet numbers to their respective interfaces. Thus, router R1 assigns subnet numbers x.0, y.0 and z.0 to its interfaces 1, 2 and 3, respectively. Similarly, router R2 assigns subnet numbers v.0, x.0 and w.0 to its interfaces 1, 2 and 3, respectively. FIG. 1a shows the respective routing tables of routers R1 and R2. Note that each routing table identifies the destination associated with each interface, the gateway associated with each destination, as well as a metric that prescribes the number of hops required to reach the destination. Note that in the initial case (FIG. 1a) all destinations associated with each router can be reached in one hop.
Now, assume that the networks are connected as at X, as shown in FIG. 1b. That is, interface 3 of router R1 is now connected to interface 1 of router R2. According to standard RIP, version 2, protocol, the routers will exchange RIP packets in the prescribed process by which the routers learn the new routes. FIG. 1b shows the routing table entry (RTE) records contained in the RIP packets sent between routers R1 and R2. Note that each router sends an RIP packet to the other router, in effect, exchanging information about the new routes. When the routers receive the RIP packets from each other, they calculate new routing tables that are augmented with the new routes just learned. FIG. 1b shows the new routing tables associated with each router. Notice that there is no way for router R2 to detect that router R1 is using subnet x.0 on its interface one for this reason. When the RIP packet from router R1 is received, router R2 assumes that the subnet x.0 specified in the RIP packet refers to the same subnet that router R2 has assigned on interface two. Because subnet x.0 is directly connected to router R2, the subnet x.0 specified within the RIP packet is discarded under standard RIP handling protocol because it has a higher cost (larger number of hops). When router R1 receives the RIP packet from router R2 it conducts a similar calculation and does not change its subnet assignment on interface one.
At this point, there are two segments in the network that use the same subnet number, namely, x.0. The hosts at network x.0 of router R1 are not visible from any host connected to router R2, and vice versa. In order for correct operation of the network, this subnet conflict in the new network must be resolved. For consistency, both routers may change their subnet assignment x.0 to new unique subnet numbers to thus bring the network to a consistent state. However, as the above example shows, standard RIP protocol cannot detect and resolve subnet conflicts.
The present invention addresses the foregoing issue by providing an improved protocol, termed zeroconfiguration routing information protocol (ZRIP), which solves the above-illustrated problems while retaining compatibility with standard RIP protocol. The improved ZRIP protocol includes a mechanism for detecting subnet conflicts as well as mechanisms for subsequent conflict notification and resolution. Using the improved protocol, a system of routers can be autoconfigured while supporting address remapping and name-to-address resolution across the network.
For a more complete understanding of the invention and its objects and advantages, refer to the following written description and the accompanying drawings.